Evolutionary significance of dipnoi

Affinities of Dipnoi or lungfishes towards fishes and amphibians and their phylogenetic relationship and position with respect to Chordates diversification.
They are not the father of amphibians rather they are the uncle of amphibians.
They might have originated from Latimaria like ancestor.
Moreover it is now confirmed that Dipnoi, Crossopterygii and Labirynthodint amphibians are originated from the common ancestor.

1. Evolutionary
significance of Dipnoi
Arethe lung fishes the
ancestor of amphibians?

2. Content
1.Introduction
2.Distribution
3.Primitive characters of Dipnoi
4.Specialized characters of Dipnoi
5.Affinities of dipnoi
1.Affinities with fishes
2.Affinities and dissimilarities with Amphibia
6.Conclusion
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4. Introduction
•Dipnoi(Gr. di-two, pnoe-breathing)is a small order of fresh water bony fishes.
•They are a group of sarcopterygiianfish, are commonly known as the lungfish.
•They respire by gills and lungs.
•Dipnoievolved during Devonian period.
•They are characterized by short jaws, crushing plate like teeth, internal nares,
reduced exo-and endo-skeleton, and diphycercal tail.
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5. Distribution
•Modern lung fishes show discontinuous distribution.
•The three surviving genera of lung fishes are Neoceratodus, Protopterusand Lepidosiren.
All are inhabitants of river.
•Neoceratodusis found only in the Burnett and Mary rivers of Queens-land in
Australia, so commonly called as ‘Burnett Salmon’ or Australian lungfish.
•Protopteruslives in large lakes and rivers of tropical Africa. It is commonly called as
‘Nile lungfish’ or African lung fish.
•Lepidosirenis found in river Amazon and Paraguay basin in South America.
•It is commonly called as ‘Amazon lungfish’ or South American lungfish.
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7. Primitive characters
1. Unconstrictednotochord.
2. Presence of cloaca.
3. Spiral valves in intestine.
4. Valves in the conus.
5. Diphycercal tail.
6. Ventral inferior nostril.
7. Persistent notochord without any
constriction.
8. Cartilaginous autostylicskull.
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8. Specialized characters
1. Internal nares, possibly help in breathing
through the nose.
2. Respiration by lungs (modified air bladder)
in addition to gill-respiration.
3. Auricle is partly divided into two and nearly
three-chambered heart.
4. One of the paired auricles receives
oxygenated blood through a special
pulmonary arch from the lungs.
5. Conus arteriosus spirally twisted and
contractile in nature.
6. Separation of pulmonary and systemic
circulation.
7. Large paired cerebral hemispheres.
8. Well-developed Mullerian duct.
9. Presence of characteristic tooth plates,
used for crushing of shelled invertebrates.
10. Bones absent in the jaw.
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9. Affinities of Dipnoi
Relationshipwithothergroupofanimals
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10. Affinities of Dipnoi
•To study the evolutionary significance of any organisms, first we have to
study their different characters.
•Then we have to compare their characters with other groups of organisms to
find out the degree of similarities and dissimilarities of that organism with
others.
•Accordinglywecanpredicttheirevolutionarypositionandtheir significance
or roll in phylogenetic diversification.
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11. Affinities with fishes
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12. General affinities with fishes
1. Spindle-shaped, eel-like body.
2. Body covered with scales
(Cycloid).
3. Presence of paired fins.
4. Diphycercal caudal fins.
5. Persistent notochord.
6. Skull with little ossification.
7. Paired gill-slits.
8. Branchial respiration.
9. Lateral line sense organs.
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13. Affinities with Elasmobranchi
1. Endoskeleton mostly cartilaginous.
2. Intestine with spiral valves.
3. Conus arteriosus with valves.
4. Each gill with two efferent arteries.
5. Absence of nephrostomein uriniferous tubules.
6. Small diencephalon with vascular roots.
7. Similar female reproductive organs.
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14. Affinities with Holocephali
1. Excurrent nostrils opening into mouth cavity.
2. Autostylicjaw suspensorium.
3. Gills covered with operculum.
4. No distinct stomach.
5. Intestine with a spiral valve.
6. Teeth fused to form dental plates.
7. Identical kidneys, gonads and gonoducts.
8. Two efferent arteries in each gill.
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15. Affinities with Actinopterygii
1. Blunt snout with ventral nostril.
2. Presence of cycloid scales.
3. Strong palate and splenial teeth.
4. Presence of operculum covering gills.
5. Presence of swim bladder.
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16. Affinities with Crossopterygii
1. Diphycercal caudal fin.
2. Powerful leg-like lobate fins.
3. Identical skull bones.
4. Vertebral column uptothe tip of caudal fin.
5. Air bladder for pulmonary respiration.
6. Internal nostrils.
7. Presence of contractile conus arteriosus.
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17. Affinities with Amphibia
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18. Similarieswith Amphibia
1. Semiaquatic habitat.
2. Internal nostrils
3. Vomerine teeth.
4. Autostylicjaw suspensorium.
5. Multicellular cutaneous glands.
6. Pulmonary respiration.
7. Dermal scales as in Apoda.
8. Ventral aorta short or absent
9. Presence of anterior abdominal vein,
posterior vena cava, pulmonary artery
and veins.
10. Thin walled pericardium.
11. Long and narrow cerebral
hemispheres.
12. Similar structure of egg and
development
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19. Dissimilarities with Amphibia
1. Paired lobate-fins
2. Maxillae and premaxillae are absent.
3. Peculiar crushing tooth plates.
4. Few anterior vertebrae fused with skull.
5. Cartilagenousskull.
6. Lungs lie dorsal to gut.
7. Urinary bladder from dorsal wall of cloaca.
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20. Conclusion
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21. Conclusion
•The above affinities indicate that dipnoans are not most advanced Pisces from which amphibians could
evolve. They are degenerate descendants of Crossopterygii.
•According to Jarvik(1968) dipnoans are more specialized than crossopterygian.
•According to latest view, both dipnoans and amphibians have originated from some crossopterygian
like ancestor.
•There must have been a common ancestor for Dipnoi, Crossopterygiiand Labyrinthodont amphibia.
•So most probably, dipnoans are not the “fathers of the amphibia”, but “uncles of the amphibian”.
•However, Jarvik(1980) considers that the Dipnoimay be related to elasmorbranchsthan any other
animals.
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